1. Field of the Invention
The present invention relates to a heat resistant vermiculite shaped product which comprises thin leaves of vermiculite and to a method for producing such product.
2. Description of the Prior Art
Conventionally, vermiculite, which is a flaky mineral, is subjected to heat treatment or the like to be expanded among layers thereof and to be exfoliated. The exfoliated vermiculite is then crushed to obtain thin leaves of vermiculite, and the thin leaves are formed into various shapes.
The thus-obtained formed products have heat resistance and are thus widely used for heat-insulating material for heat-treating furnaces or the like, sealing material, etc. However, the prior art formed products have poor compressibility and, therefore, even when they are put to use as heat-insulating or sealing material, their utility is limited.
An attempt to improve compressibility of the formed product has also been proposed. According to this attempt, thin leaves of vermiculite, obtained by the aforesaid expansion and crushing and/or organic or inorganic fiber, such as glass fiber or .alpha.-sepiolite, is admixed with powder of non-exfoliated vermiculite or with thin leaves of vermiculite prepared by the exfoliation of vermiculite in the course thereof and crushing the same; the resulting mixture is then formed to obtain a shaped product. When the thus-obtained formed product is put to use, it has to be subjected to heat treatment or treated with aqueous hydrogen peroxide or the like in order to expand vermiculite among layers thereof. However, this vermiculite formed product also has poor compressibility and poor flexibility, because the degree of expansion of the thin leaves of vermiculite is not large. According to the aforesaid attempt, in addition to the aforesaid disadvantages it is difficult to obtain a formed product which can uniformly expand throughout the product. Moreover, the coefficient of expansion of the thus-produced formed product is also as small as about 2 to 3 times the thickness of the original product.
On the other hand, the formed vermiculite product according to the prior art has poor water resistance. The formed vermiculite product in this prior art maintains its shape by bonding the thin leaves of vermiculite with one another. The surface of the thin leaves of vermiculite, however, is liable to be wettable. Therefore, if water or other liquids permeate the aforesaid formed product of vermiculite, the thin leaves are swollen therewith, resulting in loss of their bonding force. As a result, the thin leaves constituting the formed vermiculite product are broken up and dispersed.